A156871 Number of nondecreasing sequences of n positive integers with reciprocals adding up to an integer.

1, 2, 5, 20, 170, 3650, 298132, 159632503

Offset

1,2

Links

Table of n, a(n) for n=1..8.

Formula

a(n) = A156869(n, 1) + ... + A156869(n, n).

Example

For n = 3, the A156871(3) = 5 sequences are (1, 1, 1), (1, 2, 2), (2, 3, 6), (2, 4, 4) and (3, 3, 3) because 1/1 + 1/1 + 1/1 = 3, 1/1 + 1/2 + 1/2 = 2 and 1/2 + 1/3 + 1/6 = 1/2 + 1/4 + 1/4 = 1/3 + 1/3 + 1/3 = 1.

Crossrefs

Cf. A002966, A156869, A280517, A280518.

Sequence in context: A159320 A184730 A181076 * A058109 A005331 A261005

Adjacent sequences: A156868 A156869 A156870 * A156872 A156873 A156874

Keyword

more,nonn

Author

Jens Voß, Feb 17 2009

Extensions

a(7), a(8) from Max Alekseyev, Jul 27 2009

Status

approved